This used to be the biggest pain in my butt until I found a
wonderful tool. 3M makes a drum out of alternating layers of
Scotch Brite pads and Sandpaper that makes the job easy. I use
two different types, a medium for really rough areas, and a
fine one for final finishing. The drum is meant to be mounted
in a drill and I use a 15k RPM corded drill. I use the drill
at high-speed and run with the grain. You will notice an immediate
difference. If you have an area with deep tracks or damage use
the medium drum first then finish with the fine drum. There
are some ramps and assemblies you can’t use these on purely
due to size. Buy a few sheets of 600 grit sandpaper and regular
Scotch Brite pads and use some elbow grease.

I strongly urge you to wear
a respirator while doing this. The drums kick out a lot of
dust that is probably comprised of a lot of things you don’t
want in your lungs.